Wiktionary
subtheme
n. A specific theme within a larger theme
Usage examples of "subtheme".
It was just a subtheme to the concerto: a few of them need to come up with a lot of cash in a hurry, so they buy out Fyres’s companies cheap, since they’re going under, anyway, then threaten people like our good Hwdfrjaanci with eviction to make them worried, then vanish so they don’t know what’s happening so they’ll panic, and then, in a day or two, our heroes will come back with offers to sell them the land at outrageous prices, in cash.
To me some of the best SF projects ever executed take on religion as a major subtheme, elevating the stories into something universal.